Transformerless UPS Equipment

Data Center UPS Equipment: Transformerless vs. Standard

Synopsis:

Transformerless uninterruptible power supplies (UPSs) can be more energy efficient and reliable than transformer-based models and are becoming more common in new construction but are less prevalent in older facilities.

The energy consumption of a conventional transformer-based UPS varies with design and operation. Newer UPS are more efficient, and operating the UPS is "eco-mode" bypasses the power to the servers around the UPS. This significantly reduces UPS losses but also reduces the power conditioning providing by running power through the UPS. Eco-mode is therefore recommended only for data centers with utility electric power quality that is consistently high enough to meeting the needs of the server without additional power conditioning. (Green Data Center News, )

Transformerless UPSs are more energy-efficient with loads over 40%, especially in energy-saver mode, with the greatest efficiency benefit at 100% load. They may therefore be most useful when using modular UPSs that are more fully loaded.

Transformerless UPSs also have a number of non-energy benefits. They are more reliable due to having fewer components. They are also better at limiting fault current and mitigating arc flash due to faster detection isolation. With an IGBT rectifier, they provide beneficial power conditioning by holding power factor up over 99%. This also holds total harmonic distortion down (under 5% at full load), so smaller filter inductors are needed. They are highly compatible with generators and avoid generator over-sizing commonly required with older UPS, saving additional energy. They can better control battery voltage, extended battery service life. Finally, they are significantly smaller and lighter than older UPS.

Transformerless UPS are available up to 300 kVA, so cover the needs of most small- to medium-sized data centers. In selecting one, be sure that it has the compact magnetics and improved airflow that make it smaller and lighter. Make sure it can feed 4-wire loads, such as 208/120 VAC and can complete transitions in about 2 milliseconds, certainly less than 10 milliseconds.

Synopsis:

Transformerless uninterruptible power supplies (UPSs) can be more energy efficient and reliable than transformer-based models and are becoming more common in new construction but are less prevalent in older facilities.

The energy consumption of a conventional transformer-based UPS varies with design and operation. Newer UPS are more efficient, and operating the UPS is "eco-mode" bypasses the power to the servers around the UPS. This significantly reduces UPS losses but also reduces the power conditioning providing by running power through the UPS. Eco-mode is therefore recommended only for data centers with utility electric power quality that is consistently high enough to meeting the needs of the server without additional power conditioning. (Green Data Center News, )

Transformerless UPSs are more energy-efficient with loads over 40%, especially in energy-saver mode, with the greatest efficiency benefit at 100% load. They may therefore be most useful when using modular UPSs that are more fully loaded.

Transformerless UPSs also have a number of non-energy benefits. They are more reliable due to having fewer components. They are also better at limiting fault current and mitigating arc flash due to faster detection isolation. With an IGBT rectifier, they provide beneficial power conditioning by holding power factor up over 99%. This also holds total harmonic distortion down (under 5% at full load), so smaller filter inductors are needed. They are highly compatible with generators and avoid generator over-sizing commonly required with older UPS, saving additional energy. They can better control battery voltage, extended battery service life. Finally, they are significantly smaller and lighter than older UPS.

Transformerless UPS are available up to 300 kVA, so cover the needs of most small- to medium-sized data centers. In selecting one, be sure that it has the compact magnetics and improved airflow that make it smaller and lighter. Make sure it can feed 4-wire loads, such as 208/120 VAC and can complete transitions in about 2 milliseconds, certainly less than 10 milliseconds.

According to field tests by the Lawrence Berkeley National Laboratory, a 70 kVA UPS of this type at 38% load would be about 85.2% efficient with a power factor of 80%. It would consume an average of 70 kVA * .38 * 24 * 365 * .8 / .852 = 218,794 kWh per year. (LBNL, 2005 Pg 36)

Manufacturer's Energy Savings Claims:

"Typical" Savings: 3%Savings Range: From 1% to 4%

Comments:

According to Emerson (Emerson Network Power, 2013 Pg 2), the efficiency improvement resulting from switching from a transformer UPS to a transformerless UPS ranges from -1% at 30% load to about 4% at 100% load. According to Eaton, (Eaton, 2013 Pg 2), this range is 2-4%. Emerson seems to promote transformerless UPS and feels that some other manufacturers boost efficiency gains but running the server load during normal operation on the bypass rather than running all the power through the UPS, which they feel may impact availability.

Cost Effectiveness:

Cost Effectiveness is calculated using baseline energy use, best estimate of typical energy savings, and first cost. It does not account for factors such as impacts on O&M costs (which could be significant if product life is greatly extended) or savings of non-electric fuels such as natural gas. Actual overall cost effectiveness could be significantly different based on these other factors.